1. Field of the Invention
The present invention relates to a robot system for grasping and moving an operation target, and a control apparatus, method, and program thereof.
2. Description of the Related Art
Industrial robots have been introduced into production sites for various purposes, such as to stably produce high-quality products, and to release people from dangerous operations and operations that cause fatigue.
Conventionally, simple, repetitive tasks have been performed by attaching a hand for grasping an operation target on an arm of the robot, moving the arm along a predetermined course, and making the hand perform a grasping operation. Examples of simple tasks include the conveyance and sorting of operation targets, and the fitting and assembly with other operation targets.
For instance, the conveyance of a part is used as an example. Since the part is placed on a predetermined position on a parts supply pellet, first, the arm is moved to a position where the part can be grasped by the hand. Next, the part is grasped by moving the hand, and the part is then conveyed to a predetermined position on the pellet by again moving the arm. Then, the part is released by operating the hand.
However, unless the operation target (part) is correctly arranged on the parts supply pellet in a predetermined position and orientation, the part will not be completely grasped, which can make it difficult to complete the operation (conveyance). Accordingly, in Japanese Patent Application Laid-Open No. 6-170771, a distance detector is provided on the hand. The part is grasped by measuring the position and orientation of the operation target immediately before it is grasped, and the position and orientation of the grasping member are matched to the position and orientation of the operation target.
However, even when the operation target is grasped while taking such a measure, the position and orientation of the operation target can deviate due to contact between the grasping mechanism of the hand and the operation target.
To improve on this situation, the measurement and correction of the position and orientation of the operation target may be performed after the operation target is grasped. In Japanese Patent Application Laid-Open No. 2009-50921, the operation is executed by, after the operation target is grasped, measuring the position and orientation of the operation target by causing the operation target to hit an object having a known position and orientation, and sequentially moving the robot to an instructed position whose deviation from the original position and orientation has been corrected. Further, in Japanese Patent Application Laid-Open No. 2009-50921, movement of the hand is controlled so as to compensate for a deviation calculated by detecting the deviation from the correct position of the operation target carried by the hand.
However, in Japanese Patent Application Laid-Open No. 2009-50921, there is the problem that cycle time increases when measuring the position and orientation of the grasped operation target, because the operation target is made to hit an object having a known position and orientation.
Further, in Japanese Patent Application Laid-Open No. 2000-71190, the compensation of the positional deviation of the operation target is performed by correcting the objective position and orientation of the hand by only the deviation amount. Usually, a multiaxis control arm-type industrial robot has an arm with a large moment of inertia in order to maintain rigidity, and also a large time constant.
Further, for example, when calculating the route-points using inverse kinematics, usually the largest time constant in a normal system is used for the time constant. Consequently, to complete correction of the position and orientation without increasing the movement time of the arm, the determination of the corrected objective position and orientation has to be completed by a time based on a value of the time constant before the predicted time of the objective is reached. Therefore, to prevent the cycle time from increasing in a system having a large time constant, such as a multiaxis control arm-type industrial robot, there is a need to resolve the problem that the time spent to measure the position and orientation of the grasped operation target and to determine the position and orientation after correction is short.
In addition, in the above-described conventional art, the positional deviation of an operation target is corrected. Therefore, there is the problem that when performing a fitting or assembly operation on another operation target, the positional deviation of another operation target cannot be corrected.
Moreover, the above-described conventional art suffers from the problems that when the positional deviation of the grasped target is large, the target may collide with an obstruction while the arm is being moved, or that the grasping operation may have to be performed again.